Button rifle barrels are normally good for around 8K if not mistreated.  Chrome bore plated button rifles, double that number instead.

As for cooking a barrel quickly, that takes mag dumps with a full auto rig to the point that you have the gas tube glowing instead.

If your barrel is chromed lined, then at 4K in a semi auto rig even with some rapid fires, your just breaking the barrel in instead.

Truth is, at 4K, would just pull the muzzle device to give the muzzle crown and inside of the Muzzle device a good cleaning, and if you have not been cleaning the bore with a good copper solvent like Sweet's, would be a good time now.

As long as the rifle is running fine and grouping, then all is good.  Ejection patterns can be effected by combination of things like the pressure of the ammunition, ejector spring tension, extractor spring tension, action spring (buffer spring) tension, gas port size, weight of the buffer & bolt carrier, etc.  Gas ports will erode, along with headspace, throats and muzzles, etc.  What you may consider is changing your action spring (buffer spring), as it has probably gotten weaker with use, and a weaker spring will cause the bolt carrier assembly to travel rearward faster.  In theory by adding a new action spring that has more tension pushing the bolt carrier assembly forward, of which will cause the bolt carrier assembly to move rearward slower.    

CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123

Not a big fan of bore snakes for rifles.  
Granted that they can get powder type fouling out quickly of the bore, and not to bad with leading in pistols,  but its the copper layer from plated/jacketed bullets they they are not good at getting out instead.  Hence you can scrub the copper out, but better to use a copper solvent that does not require a lot of scrubbing to remove the built up copper instead.

So on that note, might want to do some cleaning rod cleaning (chamber to muzzle direction only) with a good copper solvent to get the bore clean.   As for the Brake and muzzle, after the bore is clean with a good copper solvent, then soak these parts in something like hoppers with the muzzle down and the parts in the solvent for a day, then see what you can clean from the brake and muzzle device with brushes and Q-tip instead.

Hence never been a fan of muzzle devices that you can not remove, since over time, the muzzle does end up looking like this even with bore cleanings, and chances are the more sparks you are seeing out of the Brake now, is due to the increased fouling in it instead.

Heaver buffer is counter productive of the brake, since the source of felt recoil is really the mass of the buffer and bolt reciprocating instead.

Truth is, standard FS and the barrel gas port correctly sized so you don't need a lot of buffer mass to control the stroke will produce less perceived recoil isntead.  Also, ditching the dead blow effect of the buffer does wonders to reduce felt recoil as well.

So did adding in a new recoil spring and the H3 buffer get the rifle to eject rearward now instead?
I ask since often forward ejection is just the normal spent brass off the ejector/the bolt face retracting back past the back of the ejection port window on stroke, or a problem with the extractor binding in the bolt face/ the extractor not hanging onto the spent case rim on the chamber pull instead.

Hence even with the rifle over gasses, so long as the face of the bolt does not retract behind the ejection port window/the case rim does not slip off the extractor during the chamber pull, even a standard buffer has enough dead blow effect to stall the B/C out at the back of the stoke so the spent case can be pivoted off the bolt face rearward during that back of stroke stall.